The long term goal of this research is to determine the role of autoinduction or quorum sensing in the pathogenesis of P. aeruginosa. Previous studies have shown that LasR (regulatory protein) interacts with an autoinducer, PAI, to activate transcription of virulence genes (lasB, lasA, aprA, and toxA) related to tissue destruction and possibly dissemination. By studying the regulatory pathway leading to production of these virulence factors an additional autoinducer molecule was discovered, purified, and characterized which is termed factor 2. This proposal will focus on a structure-function analysis of the autoinducers, their targets, and the role that these molecules serve in transcriptional activation of various genes involved in protease production. The results will further our understanding of the regulation of virulence in P. aeruginosa and provide new insights into quorum sensing systems.